MUSEUM OF COMPARATIVE ZOOLOGY. 191 
section is at that point below the preretinal membrane where the rhab- 
domeres diminish into simple cell boundaries, and the five cells which 
make a single group are here easily distinguishable. To the left the 
rhabdomes are much larger, and have assumed their usual outlines. The 
rhabdomes have increased in size at the expense of the cells. It will be 
noticed that each of the cells present belongs to some group of rhab- 
domeres, and consequently a// are retinal cells. 
The section (Fig. 3, @) which was the next external to the one just de- 
scribed shows practically the same condition, except that, being slightly 
nearer the front of the retina, the rhabdomes are not quite so distinct, 
especially in the extreme right, where in one or two groups scarcely any 
trace of the rhabdomeres can be seen. Nevertheless, all the cells of the 
former section can be identified, and moreover between the groups in the 
upper right hand corner an additional cell is noticeable. This cell, which 
by a comparison of the two sections is seen to be a supernumerary element, 
is not a retinal (nerve-end) cell ; but since in maceration preparations the 
outer expanded ends of the pigment cells were always found near the 
preretinal membrane, there is every reason for considering this such a 
cell. Moreover, when sections nearer and nearer the preretinal membrane 
are examined, these additional cells become more numerous, until finally 
they are with difficulty distinguished from the retinal cells. The anterior 
sacs of the pigment cells, then, can be demonstrated on sections as well 
as by maceration. 
The rhabdomes never reach the anterior face of the retina, but fall 
short of it by the thickness of several sections. This space between the 
rhabdomes and preretinal membrane corresponds to the anterior zone of 
deep pigmentation seen in longitudinal sections. The pigment in this 
region is so dense that the outlines of the cells can be traced only with 
difficulty. 
The phaospheres, as Lankester and Bourne (83, pp. 185, 186) have 
called the curious bodies mistaken by Graber for nuclei, are abundant in 
the nuclear zone of the retina (Pl. II. fig. 4, pha sp.). They are as small 
as the oval nuclei around them, and often smaller, but differ from these 
in containing usually one, and sometimes two, three, or even four highly 
refractive dots. Lankester and Bourne state that they are usually behind 
the nucleus of the retinal cell. In isolated cells I have never succeeded 
in satisfactorily identifying them, therefore in Centrurus I cannot feel sure 
of their position. In one section only has a phaosphere occurred in a 
prenuclear position; in all others they have been strictly behind the 
neighboring nuclei. 
